> For the complete documentation index, see [llms.txt](https://algorithm.prettylog.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://algorithm.prettylog.com/algorithm-problems/algoexpert/medium/symmetrical-tree.md).

# Symmetrical Tree

![](/files/T54bqzDcokX16xHlbCtG)

* n, h

```jsx
// This is an input class. Do not edit.
class BinaryTree {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

exports.BinaryTree = BinaryTree;

function symmetricalTree(tree) {
  
  return validate(tree.left, tree.right);
}

function validate(left, right) {
  if (left === null && right === null) {
    return true;
  }

  if (left === null || right === null || left.value !== right.value) {
    return false;
  }

  const outer = validate(left.left, right.right);
  const inner = validate(left.right, right.left);

  return outer && inner;
}

// Do not edit the line below.
exports.symmetricalTree = symmetricalTree;
```

* iteration

```jsx
// This is an input class. Do not edit.
class BinaryTree {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

exports.BinaryTree = BinaryTree;

function symmetricalTree(tree) {

  const leftStack = [tree.left];
  const rightStack = [tree.right];

  while (leftStack.length > 0) {
    const left = leftStack.pop();
    const right = rightStack.pop();

    if (left === null && right === null) continue;
    if (left === null || right === null || left.value !== right.value) return false;

    leftStack.push(left.left);
    leftStack.push(left.right);
    rightStack.push(right.right);
    rightStack.push(right.left);
  }

  
  return true;
}

// Do not edit the line below.
exports.symmetricalTree = symmetricalTree;
```